1. Technical Field
The present invention relates to a powder conveying device that conveys powder such as toner by way of a conveying unit that conveys the powder in a first direction and a conveying unit that conveys the powder in a second direction different from the first direction, and an image forming apparatus to which the powder conveying device is adopted.
2. Background Art
An image forming apparatus such as a printer or a copying machine in which an electrophotographic system is employed includes a photosensitive drum that carries an electrostatic latent image, a developing device that supplies toner (an example of powder) to the photosensitive drum to visualize the electrostatic latent image as a toner image, and a toner container that supplies toner to the developing device. The toner image on the photosensitive drum is transferred to a sheet. In an image forming apparatus that forms a full-color image, after the toner images of respective colors are primarily transferred to an intermediate transfer belt, the toner images are secondarily transferred to the sheet. In such an image forming apparatus, it may be necessary to form a conveyance path for conveying toner in the apparatus due to a layout of various devices.
For example, when the toner container and the developing device are spaced from each other, a conveyance path for conveying new toner is formed between the toner container and the developing device. Alternatively, when residual toner collected from the circumferential surface of the photosensitive drum or the intermediate transfer belt is conveyed to a collection bottle disposed away from the collection position, a conveyance path for conveying the residual toner is necessary. Such a toner conveyance path may include a vertical conveying unit and a horizontal conveying unit connected to a lower end of the vertical conveying unit. In this case, toner freely falls along the vertical conveying unit and reaches the horizontal conveying unit. In general, a conveying screw is disposed in the horizontal conveying unit, and the falling toner is conveyed in the horizontal direction to a predetermined position by the conveying screw.
In the toner conveying unit in which the horizontal conveying unit is disposed on the rear end of the vertical conveying unit, there is a problem that toner may clump together near a communication opening (a portion that joins the horizontal conveyance path) at the lower end of the vertical conveying unit, and smooth supply of toner is disturbed. This results from the fact that the conveying screw in rotation pushes back the toner near the communication opening whereby the toner forms clumps to block the conveyance path. In order to solve this problem, Japanese Patent Application Publication No. 2008-216360 discloses a technique of attaching a distortion coil spring to the conveying screw so as to vibrate with rotation of the conveying screw.
According to the configuration of Japanese Patent Application Publication No. 2008-216360, it is possible to prevent clumping of toner in a vibration range of the distortion coil spring. However, when toner clumps above the vibration range of the distortion coil spring, it is difficult to pulverize the clumps.
Thus, a method of simply inserting a coil member in the vertical conveying unit so as to make contact with the conveying screw due to its own weight and causing the coil member to oscillate in the vertical direction with rotation of the conveying screw may also be considered. However, when the coil member is brought into direct contact with the conveying screw, a screw blade portion may make contact with coil pieces at the lower end of the coil member to repel the coil pieces to produce noise. Further, the coil pieces may be caught in the conveying screw, and it may become difficult to perform satisfactory toner conveyance.